1. Key difference 1: Flexibility and Extensibility Ghost is a lightweight and flexible platform that focuses solely on blogging, allowing users to create and publish content with ease. On the other hand, Joomla! is a Content Management System (CMS) that offers more extensive functionality, including the ability to build complex websites with various types of content such as blogs, forums, and e-commerce. Joomla! provides a wide range of extensions and plugins that enhance its functionality and allows customization, giving users more flexibility in their website development.

2. Key difference 2: Target Audience Ghost primarily caters to individual bloggers, writers, and content creators who require a seamless and user-friendly interface to manage and publish their content in a minimalistic and efficient manner. In contrast, Joomla! is designed to cater to a broader audience, including businesses, organizations, and developers, who require a robust CMS that can handle complex websites with multiple contributors, custom workflows, and advanced features.

3. Key difference 3: User Interface and Ease of Use Ghost has a clean and intuitive interface that offers a simplified writing and editing experience, making it ideal for users who prefer a focused blogging platform. On the other hand, Joomla! has a more feature-rich and complex user interface, which may require a learning curve for new users. However, this complexity allows Joomla! to provide more extensive functionality and customization options.

4. Key difference 4: Community and Support Ghost has a smaller community compared to Joomla!, which means that there might be fewer resources and support available. However, Ghost has a helpful community forum and comprehensive documentation to assist users. Joomla!, being one of the most popular CMS platforms, has a large and active community of users, developers, and contributors. This leads to plenty of resources, extensions, and support available in various forms like forums, documentation, and official support channels.

5. Key difference 5: Performance and Speed Due to its lightweight nature, Ghost is known for its excellent performance and fast page loading times, ensuring an optimized user experience for visitors. On the other hand, Joomla! can be more resource-intensive, especially with complex websites and heavy customizations. However, Joomla! offers caching mechanisms and other optimization techniques to enhance the performance of the website.

6. Key difference 6: Security Both Ghost and Joomla! prioritize security, but there are slight differences in their approaches. Ghost, being a more specialized and minimalistic platform, focuses on ensuring a secure environment for blogging and publishing content, thereby reducing the number of potential vulnerabilities. Joomla!, being a full-fledged CMS, provides a wider range of features, which may increase the attack surface. However, Joomla! has a strong focus on security and regularly releases updates, patches, and security extensions to address vulnerabilities, ensuring a secure website.

In Summary, Ghost and Joomla! differ primarily in their focus, target audience, flexibility, user interface, community support, performance, and security, making them suitable for different use cases and user preferences.